1. Field of the Invention
The present invention relates to a polymer dispersed liquid crystal display device having randomly distributed liquid crystal molecules which cause incident light to be scattered.
2. Description of the Related Art
A liquid crystal display device comprises a liquid crystal inserted between a pair of plates having electrodes. The liquid crystal is generally used so that liquid crystal molecules are aligned in a predetermined direction. In a twisted nematic type liquid crystal display device, for example, a pair of plates which carry the liquid crystal therebetween are rubbed in directions perpendicular to each other, and thus liquid crystal molecules are aligned along the rubbing directions of the respective plates. In contrast, there is a polymer dispersed liquid crystal display device having randomly distributed liquid crystal molecules.
In a twisted nematic type liquid crystal display device, it is known that a contrast of a picture is reduced when the display is viewed from a specified viewing angle relating to the orientating direction of the liquid crystal molecules, since the liquid crystal molecules are aligned in the predetermined direction.
In a polymer dispersed liquid crystal display device, the liquid crystal layer comprises liquid crystal capsules dispersed in the resin. The liquid crystal capsules are small grains of liquid crystal molecules gathering together upon a phase separation between the liquid crystal molecules and the resin, and the liquid crystal molecules are randomly distributed in the liquid crystal capsules. Since the liquid crystal molecules are randomly distributed in the polymer dispersed liquid crystal display device, there is no specified viewing angle such as may appear when the liquid crystal molecules are aligned in the predetermined direction.
In a typical manufacturing process of a polymer dispersed liquid crystal display device, a pair of plates having transparent electrodes are bonded together by a peripheral seal; a mixture of light curable resin material and liquid crystal material is inserted in an interior space in the peripheral seal between these plates; and the resin material is cured by irradiating a light (for example, an ultraviolet light) onto a surface of one of the plates. As the resin cures, the liquid crystal molecules in small quantities are subjected to a phase separation from the resin and gather together in small grains to become liquid crystal capsules.
Recently, there is an increasing demand for a wide range of liquid crystal display devices, such as larged displays, high definition displays, and color displays. To this end, a color filter and a black matrix are provided in one of the plates, and an active matrix driver is provided in the other plate. The active matrix driver includes bus lines extending longitudinally and transversely in a matrix, and small picture electrodes are arranged in areas divided by the bus lines, the picture electrodes being connected to the bus lines via transistors (TFT; Thin Film Transistors).
In a conventional manufacturing process of a polymer dispersed liquid crystal display device, when an ultraviolet light is irradiated for curing the light curable resin material to form liquid crystal capsules, the ultraviolet light is irradiated perpendicularly to the surface of the plate. However, in the case of a polymer dispersed liquid crystal display device in which a black matrix is provided in one of the plates, and an active matrix driver is provided in the other plate, it has been found that the liquid crystal capsules are not uniformly distributed between the plates.
That is, the black matrix and bus lines are formed from metal and become a shading layer when a light is irradiated. Therefore, when an ultraviolet light is irradiated from either one of the plates, the ultraviolet light is not irradiated onto the light curable resin and the liquid crystal that are located under the shading layer. Thus the light curable resin located under the shading layer is not sufficiently hardened to fully advance a phase separation and accordingly to form the liquid crystal capsules. By observation, it has been found that the region in which the liquid crystal capsules are not formed is located not only under the shading layer, but extends into the area of the picture electrode. Accordingly, there is a portion in which the liquid crystal capsules do not exist, and a problem arises that contrast is reduced and brightness is also reduced.